In recent years, liquid crystal display devices have been widely used for liquid crystal televisions, monitors, cellular phones, and the like as flat-panel displays that have advantages such as thinner-profile and lighter-weight as compared with conventional cathode-ray displays, for example. In such liquid crystal display devices, a device using an active matrix substrate for a liquid crystal panel, which is a display panel, is known. In the active matrix substrate, a plurality of data wiring lines (source wiring lines) and a plurality of scan wiring lines (gate wiring lines) are arranged in a matrix, and pixels that respectively include switching elements such as thin-film transistors (hereinafter abbreviated as “TFTs”) and pixel electrodes connected to the switching elements are arranged in a matrix near the respective intersections of the data wiring lines and the scan wiring lines.
In such an active matrix substrate, in addition to the thin-film transistors for driving pixels as switching elements, thin-film transistors for peripheral circuits are generally disposed in an integral manner. Further, as the active matrix substrate for a liquid crystal display device with a touch panel or for a liquid crystal display device with an illuminance sensor (an ambient sensor) and the like, an active matrix substrate that has, in addition to the thin-film transistors for driving the pixels and for the peripheral circuits, photodiodes (thin-film diodes; TFDs) disposed integrally therein as photosensors has been disclosed. As described above, semiconductor devices that include a plurality of thin-film transistors and photodiodes are used in the active matrix substrate.
In such a semiconductor device, a reduction in a leak current of the thin-film transistor (transistor) has been increasingly sought after in recent years so as to satisfy the demand for the lower power consumption in a liquid crystal panel having the built-in photosensors, a liquid crystal panel having a built-in pixel memory, and the like, for example.
In response, a conventional semiconductor device that is configured such that a first light-shielding film is provided below the thin-film transistor, and a second light-shielding film is provided between the thin-film transistor and the first light-shielding film has been disclosed as described in Patent Document 1 below, for example. This conventional semiconductor device is configured such that, even when light incoming from the rear surface side of the active matrix substrate was reflected by a black matrix film, data wiring lines, or the first light-shielding film, the light is blocked by the second light-shielding film, and therefore, the leak current is reduced. In addition, the conventional semiconductor device is designed to increase ON current by forming the second light-shielding film of a material with electrical conductivity and by electrically connecting the gate wiring lines to this second light-shielding film so as to form a dual-type thin-film transistor that uses the second light-shielding film as the bottom gate electrode.